trouble in uniqueidentifier

[alecarnero]

I have write this procedure
ALTER PROCEDURE dbo.proba (@ident uniqueidentifier)

AS SELECT ident, nome FROM dbo.nomes WHERE (ident = @ident)


Private Sub Form_Open(Cancel As Integer)
Dim rsn As ADODB.Recordset
Dim identi As Variant
identi = "{3AB65B0A-60ED-4708-B492-85C56E880946}"
Set rsn = New ADODB.Recordset
rsn.Open "exec proba @iden='" & identi & "'", cn, adOpenKeyset,
adLockOptimistic
Set Forms!auxpro.Recordset = rsn
End Sub

when i try to execute this code in VB returns error of argument, what is
wrong with the code , if the procedure works fine